U.S. patent application number 11/518383 was filed with the patent office on 2008-03-13 for providing reachability information in a routing domain of an external destination address in a data communications network.
This patent application is currently assigned to CISCO TECHNOLOGY, INC.. Invention is credited to Stewart F. Bryant, Clarence Filsfils, Gargi Nalawade, Keyur Patel, Stefano B. Previdi, Robert Raszuk, Mike Shand, David D. Ward.
Application Number | 20080062986 11/518383 |
Document ID | / |
Family ID | 39169591 |
Filed Date | 2008-03-13 |
United States Patent
Application |
20080062986 |
Kind Code |
A1 |
Shand; Mike ; et
al. |
March 13, 2008 |
Providing reachability information in a routing domain of an
external destination address in a data communications network
Abstract
An apparatus for providing reachability in a routing domain of a
data communications network having as components nodes and links
therebetween for a routing domain--external destination address is
described. The apparatus is arranged to advertise destination
address reachability internally to nodes in the routing domain and
associate a reachability category with said internal advertisement
of said destination address reachability.
Inventors: |
Shand; Mike; (Cobham,
GB) ; Bryant; Stewart F.; (Merstham, GB) ;
Ward; David D.; (Los Gatos, CA) ; Nalawade;
Gargi; (San Jose, CA) ; Patel; Keyur; (San
Jose, CA) ; Filsfils; Clarence; (Brussels, BE)
; Previdi; Stefano B.; (Rome, IT) ; Raszuk;
Robert; (Komorow, PL) |
Correspondence
Address: |
HICKMAN PALERMO TRUONG & BECKER, LLP
2055 GATEWAY PLACE, SUITE 550
SAN JOSE
CA
95110
US
|
Assignee: |
CISCO TECHNOLOGY, INC.
|
Family ID: |
39169591 |
Appl. No.: |
11/518383 |
Filed: |
September 8, 2006 |
Current U.S.
Class: |
370/392 ;
370/401 |
Current CPC
Class: |
H04L 45/04 20130101;
H04L 45/28 20130101; H04L 45/22 20130101; H04L 45/02 20130101 |
Class at
Publication: |
370/392 ;
370/401 |
International
Class: |
H04L 12/56 20060101
H04L012/56 |
Claims
1. An apparatus for providing reachability information in a routing
domain of a data communications network having as components nodes
and links therebetween for a routing domain external destination
address, the apparatus being arranged to advertise destination
address reachability internally to nodes in a routing domain and
associate a reachability category with said internal advertisement
of said destination address reachability.
2. An apparatus as claimed in claim 1 further arranged to receive
external reachability information for the external destination
address.
3. An apparatus as claimed in claim 2 further arranged to determine
a reachability category from the external reachability
information.
4. An apparatus as claimed in claim 2 in which the apparatus is an
edge router or border routers of an autonomous system and
comprising an implementation of Border Gateway Protocol.
5. An apparatus as claimed in claim 1 further arranged to receive
an internal advertisement of external destination address
reachability including a reachability category.
6. An apparatus as claimed in claim 5 further arranged to compare
the reachability category with a reachability threshold and
advertise the external destination address internally to obtain
further reachability information.
7. An apparatus as claimed in claim 6 further arranged to receive
the further reachability information and updating routing or
forwarding information with the further reachability
information.
8. An apparatus as claimed in claim 7 further arranged to forward
data using the further reachability information.
9. An apparatus as claimed in claim 6 in which the apparatus is an
autonomous system router.
10. An apparatus as claimed in claim 6 further arranged to
advertise internally a fast re-route capability.
11. An apparatus as claimed in claim 1 where the external
reachability information comprises Border Gateway Protocol
connectivity.
12. An apparatus as claimed in claim 11 where the external
reachability information is received via eBGP.
13. An apparatus as claimed in claim 1 where the reachability
category is advertised in iBGP.
14. An apparatus as claimed in claim 13 where the reachability
category is advertised in a community string.
15. An apparatus as claimed in claim 1 where the destination
address is a destination address prefix.
16. An apparatus for providing reachability information in a
routing domain of a data communications network having as
components nodes and links therebetween for a routing domain
external destination address, the apparatus being arranged to
receive an internal advertisement from a router requesting further
reachability information for an external destination address and
respond with further reachability for the address if the address is
reachable.
17. A computer readable medium comprising one or more sequences of
instructions which, when executed by one or more processors, cause
the one or more processors to perform: advertising destination
address reachability internally to nodes in a routing domain; and
associating a reachability category with said internal
advertisement of said destination address reachability.
18. An apparatus comprising: one or more processors; and a network
interface communicatively coupled to the one or more processors and
configured to communicate one or more packet flows among the one or
more processors in a network and a computer readable medium
comprising one or more sequences of instructions which, when
executed by the one or more processors, cause the one or more
processors to perform: advertising destination address reachability
internally to nodes in a routing domain; and associating a
reachability category with said internal advertisement of said
destination address reachability.
19. A method of providing reachability information in a routing
domain of a data communications network having as components nodes
and links therebetween for a routing domain--external destination
address, the apparatus being arranged to advertise destination
address reachability internally to nodes in the routing domain and
associated reachability category with said internal advertisement
of said destination address reachability.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to data
communications networks.
BACKGROUND OF THE INVENTION
[0002] The approaches described in this section could be pursued,
but are not necessarily approaches that have been previously
conceived or pursued. Therefore, unless otherwise indicated herein,
the approaches described in this section are not prior art to the
claims in this application and are not admitted to be prior art by
inclusion in this section.
[0003] In computer networks such as the Internet, packets of data
are sent from a source to a destination via a network of elements
including links (communication paths such as telephone or optical
lines) and nodes (for example, routers directing the packet along
one or more of a plurality of links connected to it) according to
one of various routing protocols.
[0004] One routing protocol used, for example, in the internet is
Border Gateway Protocol (BGP). BGP is used to route data between
routing domains such as autonomous systems (AS) comprising networks
under a common administrator and sharing a common routing policy.
BGP routers exchange full routing information during a connection
session for example using Transmission Control Protocol (TCP)
allowing inter-autonomous system routing. The information exchanged
includes various attributes including a next-hop attribute. For
example where a BGP router advertises a connection to a network,
for example in a form of an IP address prefix, the next-hop
attribute comprises the IP address used to reach the BGP
router.
[0005] Edge or border BGP routers in a first AS (ASBRs) communicate
with eBGP peers in a second AS via exterior BGP (eBGP). In addition
BGP routers within an AS exchange reachability information using
interior BGP (iBGP). As a very large number of routes may be
advertised in this manner an additional network component
comprising a route reflector is commonly provided which sets up a
session with each BGP router and distributes reachability
information to each other BGP router.
[0006] The border routers in respective AS's can advertise to one
another, using eBGP, the prefixes (network destinations) reachable
from them, the advertisements carrying information such as AS-path,
indicating the AS's through which the route advertisement has
passed including the AS in which the advertising border router
itself is located, and a BGP Community attribute indicating the
manner in which the advertisement is to be propagated. For example
if an eBGP advertisement is received with Community attribute
No-Advertise, then the border router receiving the advertisement
does not advertise the route information to any of its peers,
including other routers in its AS. When the routes are advertised
internally using iBGP, additional information such as a local
preference and a nexthop field are included. The local preference
attribute sets a preference value to use of that particular route
for example for a given set of prefixes such that where more than
one route is available to other border routers in the AS they will
select the route with the highest local preference. The next-hop
attribute provides the IP address used for the link between the
border router in the AS and its eBGP peer.
[0007] To reduce the amount of iBGP messages further, route
reflectors may only advertise the best path for a given destination
to all border routers in an AS. Accordingly all border routers will
forward traffic for a given destination to the border router
identified in the best path advertisement. Forwarding of packets
within the AS may then simply use Interior Gateway Protocol (IGP)
as described in more detail below where the IGP forwarding table
will ensure that packets destined for the eventual destination will
be forwarded within the AS towards the appropriate border router.
Alternatively an ingress border router receiving incoming packets
may tunnel the packets to the appropriate egress border router,
that is, encapsulate the packets to a destination egress border
router for example using IP or MPLS tunnels. The packets are then
decapsulated at the egress border router and forwarded according to
the packet destination header.
[0008] BGP is capable of supporting multiple address types for
example internet protocol version 4 (IPv4), internet protocol
version 6 (IPv6) and so forth, and each type of address is
identified using an address family identifier (AFI) and a
subsequent address family identifier (SAFI). The destinations
reachable via a BGP route, for example the network components whose
IP addresses are represented by one IP prefix, are referred to as
the network layer reachability information (NLRI) in BGP.
[0009] Within each AS the routing protocol typically comprises an
interior gateway protocol (IGP) for example a link state protocol
such as open shortest path first (OSPF) or intermediate
system--intermediate system (IS-IS).
[0010] The link state protocol relies on a routing algorithm
resident at each node. Each node on the network advertises,
throughout the network, links to neighboring nodes and provides a
cost associated with each link, which can be based on any
appropriate metric such as link bandwidth or delay and is typically
expressed as an integer value. A link may have an asymmetric cost,
that is, the cost in the direction AB along a link may be different
from the cost in a direction BA. Based on the advertised
information in the form of a link state packet (LSP) each node
constructs a link state database (LSDB), which is a map of the
entire network topology, and from that constructs generally a
single optimum route to each available node based on an appropriate
algorithm such as, for example, a shortest path first (SPF)
algorithm. As a result a "spanning tree" (SPT) is constructed,
rooted at the node and showing an optimum path including
intermediate nodes to each available destination node. The results
of the SPF are stored in a routing information base (RIB) and based
on these results the forwarding information base (FIB) or
forwarding table is updated to control forwarding of packets
appropriately. When there is a network change an LSP representing
the change is flooded through the network by each node adjacent the
change, each node receiving the LSP sending it to each adjacent
node.
[0011] As a result, when a data packet for a destination node
arrives at a node the node identifies the optimum route to that
destination and forwards the packet to the next node along that
route. The next node repeats this step and so forth.
[0012] It is important to minimize packet loss in the case of
network component failure, both intra-domain (eg IGP) and
inter-domain (eg BGP). For example in the case of intra domain link
failure ISP's use various techniques to react quickly to the
failure while convergence is taking place including handling of the
failures by other layers or implementing fast reroute techniques
for example of the type described in co-pending patent application
Ser. No. 10/340,371, filed 9 Jan. 2003, entitled "Method and
Apparatus for Constructing a Backup Route in a Data Communications
Network" of Kevin Miles et al., ("Miles et al."), the entire
contents of which are incorporated by reference for all purposes as
if fully set forth herein.
[0013] In the case of inter-domain failure, for example failure of
peering links between AS's, convergence can take several seconds.
In one mode of operation, in these circumstances, a BGP router
attached to a failed eBGP peering link advertises a new LSP without
the destination served by the failed link together with an iBGP
withdraw message indicating that the destinations are not
reachable. A solution to the problem of inter-domain failure has
been described in co-pending patent application Ser. No.
11/254,469, filed Oct. 20, 2005, entitled "A Method of Constructing
a Backup Path in an Autonomous System" of Clarence Filsfils et al
("Filsfils et al"), the entire contents of which are incorporated
by reference for all purposes as if fully set forth herein. As
described in Filsfils et al, in the case where an AS has links with
multiple AS's serving respective sets of destinations or prefixes,
a backup path is constructed in the case of failure of a link to a
respective one of the multiple AS's by identifying alternate links
serving the same set of destinations, providing per-prefix route
protection.
[0014] Currently, when a prefix is advertised in iBGP, the routers
contained in the AS must derive the reliability of (redundancy in)
the external connection to each prefix themselves from the number
of adverts they receive displaying connectivity to said prefix.
This leads to a computational overhead which slows down iBGP
convergence.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawings and in which like reference numerals refer to similar
elements and in which:
[0016] FIG. 1 is a network diagram illustrating a network in
relation to which the approach can be implemented;
[0017] FIG. 2 is a is a flow diagram illustrating at a high level
the steps involved in implementing the approach;
[0018] FIG. 3 is a flow diagram of the process at an ASBR;
[0019] FIG. 4 is a flow diagram of the process at a receiving node
within an AS;
[0020] FIG. 5 is a flow diagram showing the steps performed at a
further ASBR;
[0021] FIG. 6 is a schematic diagram of a network having diverse
paths from an AS to a prefix, p;
[0022] FIG. 7 is a schematic diagram of a network having a parallel
path from an AS to a prefix, p;
[0023] FIG. 8 is a schematic diagram of a network having a single
path from an AS to a prefix, p;
[0024] FIG. 9 is a schematic diagram of a network where an ASBR has
the ability to ask for help with FRR or FC assistance;
[0025] FIG. 10 is a block diagram that illustrates a computer
system on which the method of using reachability information may be
implemented.
DESCRIPTION OF EXAMPLE EMBODIMENT
[0026] An apparatus and method is described for providing
reachability information in a routing domain of an external
destination address in a data communications network. In the
following description, for the purposes of explanation, numerous
specific details are set forth in order to provide a thorough
understanding of the present invention. It will be apparent,
however, to one skilled in the art that the present invention may
be practiced without these specific details. In other instances,
well-known structures and devices are shown in block diagram form
in order to avoid unnecessarily obscuring the present
invention.
[0027] Embodiments are described herein according to the following
outline: [0028] 1.0 General Overview [0029] 2.0 Structural and
Functional Overview [0030] 3.0 Apparatus and method for providing
reachability information in a routing domain of an external
destination address in a data communications network [0031] 4.0
Implementation Mechanisms--Hardware Overview [0032] 5.0 Extensions
and Alternatives
[0033] 1.0 General Overview
[0034] The needs identified in the foregoing Background, and other
needs and objects that will become apparent for the following
description, are achieved in the present invention, which
comprises, an apparatus for providing reachability information in a
routing domain of a data communications network having as
components nodes and links therebetween for a routing
domain--external destination address. The apparatus is arranged to
advertise destination address reachability internally to nodes in
the routing domain and associate a reachability category with said
internal advertisement of said destination address
reachability.
[0035] In other aspects, the invention encompasses a computer
apparatus and a computer-readable medium configured to carry out
the foregoing steps.
[0036] 2.0 Structural and Functional Overview
[0037] In overview an apparatus and method for providing
reachability information in a routing domain such as an AS
according to the approach described herein can be understood with
reference to FIG. 1 which is a network diagram illustrating a
network in relation to which the approach can be implemented and
FIG. 2 which is flow diagram illustrating at a high level the steps
involved in implementing the approach.
[0038] The network shown in FIG. 1 includes autonomous systems AS1,
AS2, AS3 reference numerals 100, 102, 104. AS1 includes an ASBR1,
reference numeral 106 which acts as an external reachability
information receiving ASBR for the AS. AS1 further includes an
additional ASBR2 reference numeral 108 which acts as a further
external reachability information receiving node and an internal
reachability information receiving node, and an internal node or
router R1, reference numeral 110, acting as an internal
reachability information receiving and advertising node. ASBR1 is
connected to one or more ASs, AS2, AS3 providing connectivity to a
destination address such as a prefix for example p/27. It will be
appreciated that the network configuration shown, the connectivity
and the destination address itself can be of any appropriate type
and a simple configuration is provided in FIG. 1 for the purposes
of clarity of explanation.
[0039] In order to provide reachability information, at step 200,
ASBR1 receives external reachability information for example BGP
connectivity information via eBGP. This may be received in the
network of FIG. 1, for example from at least one of the ASs AS2,
AS3 in relation to an external destination address such as p/27. At
step 202 ASBR1 determines a reachability category from the received
information in relation to the external destination address.
[0040] As can be seen from FIG. 1 and as will be discussed in more
detail below, the reachability category would be dependent upon the
external connectivity, external policy and local policy. For
example in the network shown in FIG. 1, ASBR has a fully diverse
path to p/27 via either of AS2 or AS3. In the absence of AS3 ASBR1
would have a parallel path represented by dual links 114, 116 to
AS2. Alternatively again in the absence of AS2, ASBR1 would have
only a single path 118 to p/27 via AS3.
[0041] At step 204 ASBR1 advertises the destination address
reachability internally to nodes in the AS for example via iBGP. At
step 206 the determined reachability category is associated with
the internal advertisement for example as part of the iBGP
advertisement in a community string. As a result a node receiving
the iBGP advertisement in the network for example node R1 is able
to derive additional connectivity information in relation to p/27
for example by comparison to a policy defining a threshold.
[0042] Accordingly at step 208 node R1 is able if necessary to
advertise for further connectivity information. For example where
the category was advertised in the form of an indicator indicating
that only a single path is available to p/27 from ASBR1, router R1
may issue an internal advertisement seeking ASBRs within AS1 which
also provides connectivity to p/27. For example referring to FIG. 1
ASBR2 may also provide connectivity albeit via additional hops 120,
122 and AS2. ASBR2 responds to the advertisement from R1 at step
210 and at step 212 the router can install this alternate path for
example as a fast reroute path in the event of failure of ASBR or
as a fast convergence path as appropriate. Indeed, in the former
case, the advertisement from the router can additionally indicate
that it is fast reroute capable and this can be factored into the
response from the further ASBR2 providing additional connectivity
information. Accordingly when connectivity failure to p/27 takes
place then, at step 214, the router forwards affected packets via
the alternate path.
[0043] Accordingly it will be seen that both an ASBR such as ASBR1
and an internal router such as node R1 can provide reachability
information relating to an external destination address, to other
internal nodes, and to further ASBR's. In addition one or more
further next best alternate paths can be advertised with a
corresponding reachability category.
[0044] The addition of the BGP community string indicators reduces
the computational overhead on iBGP convergence and provides
information on suitable FRR paths. Network
stability/reliability/redundancy/connectivity in the case of a link
or node failure is enhanced with the prior knowledge of the
existence of alternate paths and the ability to request help in
finding an alternative path and the offer of being FRR capable.
[0045] 3.0 Apparatus and Method for Providing Reachability
Information in an Autonomous System of an External Destination
Address in a Data Communications Network
[0046] Reference is made to FIG. 3 which is a flow diagram of the
process at an ASBR such as ASBR1, FIG. 4 which is a flow diagram of
the process at a receiving node within an AS and FIG. 5 which is a
flow diagram showing the steps performed at a further ASBR such as
ASBR2.
[0047] Referring firstly to FIG. 3, at step 300, incoming eBGP
adverts are received at ASBR1 from ASBRs of other ASs in the data
communications network and, via iBGP, from other ASBRs in its own
AS. At step 302, the receiving ASBR collates all the incoming
adverts and builds up knowledge of the network address prefixes it
has connectivity or reachability to and determines the nature of
the reachability to each individual prefix. According to the
reachability derived, a category or indicator is assigned to each
reachable individual network address prefix as discussed in more
detail below. At step 306 an IBGP advertisement for the respective
prefix is constructed and the indicator is placed within the
community string field of the iBGP message.
[0048] At step 308 the receiving ASBR advertises the enhanced
connectivity information using IBGP internally within AS1.
[0049] The category can indicate, for example, the level of
redundancy available in connectivity between the ASBR and the
prefix. FIG. 6 is a schematic network diagram illustrating one
possible scenario where ASBRs X and Y, 602 and 614 contained within
ASs AS2 and AS3, 600 and 612 each advertise in eBGP connectivity
information to a prefix,p 608. ASBR1 606 contained within AS1 604
receives these adverts and concludes that it has completely diverse
paths to prefix, p via ASBRX 602 in AS2 600 or ASBRY 614 in AS3
612. This provides protection against both link failure between AS1
604 and one of AS2 and AS3 600 and 612 and failure of either ASBRX
602 or ASBRY 614. AS1 604, therefore, is provided with connectivity
to prefix, p that is diverse against any failure except the failure
of AS1 604 itself. Routers residing in AS1 604 are given knowledge
of this diverse path to prefix p by ASBR1 606 advertising prefix, p
in iBGP accordingly 610 via the community string indicator as
described above.
[0050] An alternative scenario can be understood with reference to
FIG. 7 which is a schematic network diagram. In particular ASBR1
706 in AS1 704 identifies parallel paths to ASBRX 702 in AS2 700.
Hence ASBR1 will advertise, together with the prefix advertisement
in iBGP, an indicator indicating that parallel paths are
available.
[0051] A further scenario is shown in FIG. 8 which is an
illustrative network diagram. In this case ASBR1, 806 in AS1 804
has a single path to prefix P via ASBRX 802 in AS2 800. Once again
the fact that only a single link is available is advertised in
conjunction with the iBGP advertisement.
[0052] It will be noted that the specific form of the indicator can
take any appropriate type such as setting of one or more
appropriate bits, or any other appropriate coding recognisable by
the other components in the AS. It will be noted that an indicator
associated with a particular prefix does not necessarily accurately
represent the actual network arrangement. To accommodate this, an
ASBR may in effect set a particular path to a network address
prefix as optimum or non-optimum by setting a corresponding
indicator regardless of the actual network arrangement and the
router will then take appropriate action in a policy dependent
manner as discussed below.
[0053] Turning to the steps performed at a router R1 in AS1 as
shown in FIG. 4, at step 400 the IBGP advert including the enhanced
connectivity information in the form of the category indicator is
received by a router R1 internal to AS1. At step 402 R1 updates its
RIB (which then leads to the FIB being subsequently updated)
according to normal operation, and at step 404 R1 examines the
category indicator.
[0054] The router R1 may have prior knowledge of the degree of
reachability required for each individual network address prefix it
has access to for example in the form of a policy and can compare
this with the advertised enhanced connectivity information. The
steps taken in relation to the reachability category for a given
prefix may then be determined according to the policy. For example
in all cases the router may require at least one further path as
well as additional paths if there is a single point of failure. In
the embodiment described herein, however, in the case of a "diverse
connectivity" indicator (the scenario at FIG. 6), no further backup
information is generally required as redundancy already exists in
the path. Routers within AS1 604 who have visibility to the iBGP
advert and who are satisfied with this level of protection need
take no further action regarding path protection.
[0055] In the case of the scenario shown in FIG. 7, where ASBR1
advertises parallel prefixes to prefix p, routers may elect to rely
on that redundancy and not seek further protection paths according
to the embodiment described herein or may take other action if
additional paths are considered to be required.
[0056] Referring to the scenario shown in FIG. 8 in which only a
single path is available from ASBR1 to prefix p this is indicated
correspondingly in the iBGP advertisement. The router R1 will
recognise that this part of the network is potentially vulnerable
as a single point of failure.
[0057] Reverting to FIG. 4, if a particular prefix may only be
reached through such a path, and furthermore, this is deemed
insufficient, the router at step 406 advertises the address in iBGP
with the indicator in the enhanced connectivity information
indicating the use of a single path and the need for a backup path
to obtain FRR or FC assistance. In FC additionally, if a router is
FRR capable, it may append a further indicator that it is FRR
capable to the enhanced connectivity information stored in the
community string of the iBGP advert 408. The enhanced connectivity
information is then re-advertised by that router using iBGP
410.
[0058] At step 412 the router receives a response from the ASBR
providing alternate connectivity and at step 414 the router holds
the information in the RIB (in the case of fast convergence) or the
presence of the alternative route can be used to speed up
convergence by switching immediately to it before waiting for the
full BGP convergence. If the information if FRR capable the node
can actually repair to it immediately updates its forwarding tables
appropriately (in the case of fast re-route) for example by
providing the alternate nexthop for the alternate computed path for
use in the event of notification of withdrawal of the primary
route.
[0059] FIG. 5 shows the steps at an ASBR that receives a `help`
request. At step 500 the ASBR, for example ASBR2 in FIG. 1,
receives the enhanced information including the "help" indicator
that a router requires further connectivity following review of the
category indicator it received via IBGP from the ASBR1. At step 502
ASBR2 assesses whether it can provide any connectivity to the
advertised destination and if so responds to the advertising AS.
Again, this transaction can be conducted using iBGP. Indeed ASBR2,
upon receipt of a single path indicator ASBR2 can immediately
advertise its alternate route for the prefix via IBGP.
[0060] The "help" indicator can be further understood with
reference to FIG. 9, which illustrates a scenario where a router R1
910 within AS1 900 receives an indicator that prefix, p is
reachable via a single path via AS 902. R1 asks for help with
either FRR assistance or FC assistance. In order to request this
help, the router 910 alters the indicator of the prefix, p in the
IBGP message appropriately or constructs a new IBGP message and
re-advertises the prefix, p with the "help" indicator 912. Upon
receiving a prefix with a "help" indicator, another ASBR, say ASBR
906 may respond by advertising 908 a less optimum route for prefix,
p with either a single, parallel or diverse indicator and as an FRR
or FC target dependent on whether the FRR capable indicator was
set. In particular, if the router that has the alternate path is
FRR capable, it is telling the requestor that it has an alternate
(less good) path, and that if the requestor sends it a packet using
an IPFRR technique it will send the packet out of the AS--even if
it has a "better" router via the AS and another ASBR. FRR
capability is encoded within the help by mechanisms known to those
skilled in the art.
[0061] As a result forwarding is improved in the event of a failure
whilst reducing IBGP traffic and avoiding techniques such as
automatic or policy controlled addition of routes in IBGP using
techniques such as an "addpath" attribute.
[0062] The approach can be implemented in any appropriate network
or environment using any appropriate protocol. The manner in which
the method described herein is implemented may be using software,
firmware, hardware or any combination thereof and with any
appropriate code changes as will be apparent to the skilled reader
without the need for detailed description herein.
[0063] 4.0 Implementation Mechanisms--Hardware Overview
[0064] FIG. 10 is a block diagram that illustrates a computer
system 40 upon which the method may be implemented. The method is
implemented using one or more computer programs running on a
network element such as a router device. Thus, in this embodiment,
the computer system 140 is a router.
[0065] The computer system 140 implements as a router acting as an
external advertisement receiving node the above described method of
forwarding data. Computer system 140 includes a bus 142 or other
communication mechanism for communicating information, and a
processor 144 coupled with bus 142 for processing information.
Computer system 140 also includes a main memory 146, such as a
random access memory (RAM), flash memory, or other dynamic storage
device, coupled to bus 142 for storing information and instructions
to be executed by processor 144. Main memory 146 may also be used
for storing temporary variables or other intermediate information
during execution of instructions to be executed by processor 144.
Computer system 140 further includes a read only memory (ROM) 148
or other static storage device coupled to bus 142 for storing
static information and instructions for processor 144. A storage
device 150, such as a magnetic disk, flash memory or optical disk,
is provided and coupled to bus 142 for storing information and
instructions.
[0066] A communication interface 158 may be coupled to bus 142 for
communicating information and command selections to processor 144.
Interface 158 is a conventional serial interface such as an RS-232
or RS-422 interface. An external terminal 152 or other computer
system connects to the computer system 140 and provides commands to
it using the interface 158. Firmware or software running in the
computer system 140 provides a terminal interface or
character-based command interface so that external commands can be
given to the computer system.
[0067] A switching system 156 is coupled to bus 142 and has an
input interface and a respective output interface (commonly
designated 159) to external network elements. The external network
elements may include a plurality of additional routers 160 or a
local network coupled to one or more hosts or routers, or a global
network such as the Internet having one or more servers. The
switching system 156 switches information traffic arriving on the
input interface to output interface 159 according to pre-determined
protocols and conventions that are well known. For example,
switching system 156, in cooperation with processor 144, can
determine a destination of a packet of data arriving on the input
interface and send it to the correct destination using the output
interface. The destinations may include a host, server, other end
stations, or other routing and switching devices in a local network
or Internet.
[0068] The computer system 140 implements as a router acting as an
internal or external advertisement receiving node the above
described method of forwarding data. The implementation is provided
by computer system 140 in response to processor 144 executing one
or more sequences of one or more instructions contained in main
memory 146. Such instructions may be read into main memory 146 from
another computer-readable medium, such as storage device 150.
Execution of the sequences of instructions contained in main memory
146 causes processor 144 to perform the process steps described
herein. One or more processors in a multi-processing arrangement
may also be employed to execute the sequences of instructions
contained in main memory 146. In alternative embodiments,
hard-wired circuitry may be used in place of or in combination with
software instructions to implement the method. Thus, embodiments
are not limited to any specific combination of hardware circuitry
and software.
[0069] The term "computer-readable medium" as used herein refers to
any medium that participates in providing instructions to processor
144 for execution. Such a medium may take many forms, including but
not limited to, non-volatile media, volatile media, and
transmission media. Non-volatile media includes, for example,
optical or magnetic disks, such as storage device 150. Volatile
media includes dynamic memory, such as main memory 146.
Transmission media includes coaxial cables, copper wire and fiber
optics, including the wires that comprise bus 142. Transmission
media can also take the form of wireless links such as acoustic or
electromagnetic waves, such as those generated during radio wave
and infrared data communications.
[0070] Common forms of computer-readable media include, for
example, a floppy disk, a flexible disk, hard disk, magnetic tape,
or any other magnetic medium, a CD-ROM, any other optical medium,
punch cards, paper tape, any other physical medium with patterns of
holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory
chip or cartridge, a carrier wave as described hereinafter, or any
other medium from which a computer can read.
[0071] Various forms of computer readable media may be involved in
carrying one or more sequences of one or more instructions to
processor 144 for execution. For example, the instructions may
initially be carried on a magnetic disk of a remote computer. The
remote computer can load the instructions into its dynamic memory
and send the instructions over a telephone line using a modem. A
modem local to computer system 140 can receive the data on the
telephone line and use an infrared transmitter to convert the data
to an infrared signal. An infrared detector coupled to bus 142 can
receive the data carried in the infrared signal and place the data
on bus 142. Bus 142 carries the data to main memory 146, from which
processor 144 retrieves and executes the instructions. The
instructions received by main memory 146 may optionally be stored
on storage device 150 either before or after execution by processor
144.
[0072] Interface 159 also provides a two-way data communication
coupling to a network link that is connected to a local network.
For example, the interface 159 may be an integrated services
digital network (ISDN) card or a modem to provide a data
communication connection to a corresponding type of telephone line.
As another example, the interface 159 may be a local area network
(LAN) card to provide a data communication connection to a
compatible LAN. Wireless links may also be implemented. In any such
implementation, the interface 159 sends and receives electrical,
electromagnetic or optical signals that carry digital data streams
representing various types of information.
[0073] The network link typically provides data communication
through one or more networks to other data devices. For example,
the network link may provide a connection through a local network
to a host computer or to data equipment operated by an Internet
Service Provider (ISP). The ISP in turn provides data communication
services through the world wide packet data communication network
now commonly referred to as the "Internet". The local network and
the Internet both use electrical, electromagnetic or optical
signals that carry digital data streams. The signals through the
various networks and the signals on the network link and through
the interface 159, which carry the digital data to and from
computer system 140, are exemplary forms of carrier waves
transporting the information.
[0074] Computer system 140 can send messages and receive data,
including program code, through the network(s), network link and
interface 159. In the Internet example, a server might transmit a
requested code for an application program through the Internet,
ISP, local network and communication interface 158. One such
downloaded application provides for the method as described
herein.
[0075] The received code may be executed by processor 144 as it is
received, and/or stored in storage device 150, or other
non-volatile storage for later execution. In this manner, computer
system 140 may obtain application code in the form of a carrier
wave.
[0076] 5.0 Extensions and Alternatives
[0077] In the foregoing specification, the invention has been
described with reference to specific embodiments thereof. It will,
however, be evident that various modifications and changes may be
made thereto without departing from the broader spirit and scope of
the invention. The specification and drawings are, accordingly, to
be regarded in an illustrative rather than a restrictive sense.
[0078] Any appropriate routing protocol and mechanism and
forwarding paradigm can be adopted to implement the invention. The
method steps set out can be carried out in any appropriate order
and aspects from the examples and embodiments described juxtaposed
or interchanged as appropriate. For example the method can be
implemented using link state protocols such as intermediate
system-intermediate system (IS-IS) or open shortest path first
(OSPF), or routing vector protocols and any forwarding paradigm,
for example MPLS. The method can be applied in any network of any
topology and in relation to any component change in the network for
example a link or node failure, or the introduction or removal of a
network component by an administrator.
[0079] Furthermore, the mechanism above of identifying network
prefix address connectivity in the Community string of BGP is
potentially usable in other protocols where a proportion of the
protocol is reserved for the transport of network and connectivity
information.
[0080] Where reference is made to BGP, eBGP or iBGP it will be
appreciated that the approach can be applied in relation to any
appropriate exterior or inter-domain protocol. The routing domain
may comprise an AS, SRLG, or LAN, or any other network of
interconnected components sharing a common routing protocol.
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